I was scratching my head for a few minutes over the g++ error message in the title. Google turned up a couple of red herrings, like this one at Stack Overflow where a clueless noob #defined the name of his class.

My mistake had been to define a constructor without putting the Class:: in front of it:

Class() // WRONG!!!
: Super(), _duper()
{
}

instead of

Class::Class()
: Super(), _duper()
{
}

It wasn't as stupid as it sounds, I was cutting and pasting inlined functions into the .cpp file.